1. Field of the Invention
The present invention relates to a magneto-optical recording medium and a layer structure and is in particular useful as a technique of achieving an increase of a Kerr rotation angle and improvements of a recording sensitivity and a recording density.
2. Description of the Related Art
Conventionally, as magneto-optical recoding media, magnetic optical (MO) discs and mini discs (MDs) have been developed and commercialized. In the case of such a magneto-optical recording medium, a Kerr rotation angle at the time of irradiation with reproduction light influences the SNR (Signal to Noise Ratio) of a reproduction signal, so various techniques of increasing the Kerr rotation angle have been studied heretofore.
For instance, in a prior art (Prior Art 1) described in JP 2004-30717 A, by improving the composition and layer construction of a recording layer, lowering of the Kerr rotation angle with respect to blue laser light is suppressed. That is, the composition of an RE-TM alloy constituting the recording layer is set TM-rich, an antiferromagnetic layer is formed on the recording layer, and a flattening layer having superior surface smoothness is formed as a primary coating of the antiferromagnetic layer as a countermeasure against surface roughness due to the formation of the antiferromagnetic layer. Aside from this, a method is also considered with which by repeatedly reflecting laser light with a dielectric layer (multiple reflection), the Kerr rotation angle is increased.
Also, various techniques of improving the recording sensitivities of the magneto-optical recording media are studied. For instance, in a prior art (Prior Art 2) described in JP 11-353725 A, a recording auxiliary layer and a ferromagnetic layer are arranged in addition to a recording layer. According to this prior art, a magnetic field at the position of the recording layer is increased through generation of a magnetic field by the recording auxiliary layer from an external magnetic field and concentration of a magnetic flux by the action of the ferromagnetic layer, thereby an improvement of a recording sensitivity is achieved.
Further, various techniques of improving the recording densities of the magneto-optical recording media are studied. For instance, in a prior art (Prior Art 3) described in JP 2003-109247 A, by forming minute recording cells while separating them from each other with non-recording areas, an improvement of a recording density is achieved.
According to Prior Art 1 described above, however, it is required to set the composition of the recording layer TM-rich and additionally arrange the antiferromagnetic layer and the flattening layer, so a limitation is imposed on the flexibility of a medium construction and there is a possibility that a demerit in terms of cost will occur. In addition, when the method is used with which the dielectric layer is additionally arranged, the number of manufacturing steps is increased accordingly, so there occurs a problem in that a cost is increased and a limitation is imposed on the flexibility of a medium construction like in the case of Prior Art 1.
Also, according to Prior Art 2 described above, it is required to additionally arrange the recording auxiliary layer and the ferromagnetic layer in order to improve the recording sensitivity, so there occurs a problem in that manufacturing steps become complicated.
Further, according to Prior Art 3 described above, it is required to form the recording cells while separating them from each other with the non-recording areas in order to improve the recording density, so there occurs a problem in that complication of manufacturing steps and an increase in cost are inevitable.